1. Field of the Invention
This invention relates to a catalyst for the production of ethylene oxide, a method for the production of the catalyst, and a method for the production of ethylene oxide. It relates more particularly to a silver catalyst which excels in catalytic activity, selectivity, and service life and permits production of ethylene oxide at high selectivity for a long time, a method for the production thereof, and a method for the production of ethylene oxide by the use of this silver catalyst.
2. Description of the Related Art
The production of ethylene oxide by the catalytic vapor phase oxidation of ethylene with a molecular oxygen-containing gas in the presence of a silver catalyst is widely practiced on a commercial scale. Concerning the silver catalyst to be used for the catalytic vapor phase oxidation, numerous inventions covering carriers for the catalyst, methods for depositing the catalyst on such carriers, and reaction promoters used therein have been applied for patent.
U.S. Pat. No. 5,077,256, for example, discloses an idea of using a carrier which is formed by superposing a coating layer of amorphous silica on an .alpha.-alumina carrier. JP-A-02-363,139 discloses an idea of using a carrier which is obtained by adding to an .alpha.-alumina a compound of one member or two or more members selected from the class consisting of the elements falling in the fourth, fifth, and sixth periods and the IIIa-VIIa and IIIb-Vb groups of the periodical table of the elements (such as, for example, titanium, tin, and hafnium) and calcining the superposed layers.
Though the silver catalysts proposed to date already possess highly advanced levels of selectivity, the desirability of imparting further improved selectivity to these silver catalysts has been finding recognition because the scale of production of ethylene oxide is so large that even an increase of only 1% in the selectivity may result in copiously saving ethylene as a raw material and consequently bring a large economic effect. In the existing circumstances, the development of a silver catalyst possessing a better catalytic efficiency has posed a lasting theme for researchers in the relevant technical field.
The silver catalysts which are disclosed in the patent publications mentioned above, however, are still deficient in selectivity and are not satisfactory in terms of service life.
It is, therefore, an object of this invention is to provide a silver catalyst which possesses an excellent catalytic capacity and permits production of ethylene oxide at a high selectivity for a long time, a method for the manufacture thereof, and a method for the production of ethylene oxide by the use of the silver catalyst.